Q 2.11 How are satellites launched?
Geostationary satellites can be launched directly into orbit. However, it is usual to launch them in a sequence outlined below. Velocity increment is least when a satellite is launched from a parking orbit to an intermediate elliptical orbit known as transfer orbit which has an apogee at geosynchronous altitude and then injected into a geo-synchronous orbit. This principle is called Hohmann Transfer, named after the scientist who proposed the principle in 1925.
1. Launch into a parking orbit;
2. Transfer into a transfer orbit;
3. Inject into an inclined geo-synchronous orbit;
4. Make orbital adjustments such that inclination is near zero;
5. Drift satellite to desired orbital location;
6. Conduct orbital maneuvers to fix satellite at desired location.
When a satellite reaches its designated location, its solar panels are deployed, the Sun and the Earth are acquired, and communication antennas deployed. The satellite sub-systems are checked out and the satellite commissioned.
Deployment of a non-geostationary constellation quickly and economically is vital for commercial success of the system. Therefore launching of multiple satellites per launch is a common practice – existing vehicles can launch 3–12 satellites in a low Earth orbit. Satellites may be placed in low or medium Earth orbit directly or via a parking orbit. Typically, a launcher deposits clusters of satellites at regular intervals in a parking orbit. When a precise orbital position of each cluster has been determined, each satellite within is maneuvered to the desired altitude and inclination by firing onboard thrusters for a specific duration at an appropriate time. Support of a network of tracking stations dispersed throughout the world is essential to accomplish the desired goal.